The separation and detection of biological cells and biomolecules, such as red blood cells, white blood cells, platelets, proteins, DNAs, and RNAs, have become more and more important to biological assays crucial to fields such as genomics, proteomics, diagnoses, and pathological studies. For example, due to faster and more specific methods of separating and detecting cells and biomolecules, the molecular-level origins of disease are being elucidated at a rapid pace, potentially ushering in a new era of personalized medicine in which a specific course of therapy is developed for each patient. To fully exploit this expanding knowledge of disease phenotype, new methods for separating and detecting multiple cells and biomolecules (e.g., DNA and proteins) simultaneously are required. In many cases, separation and detection of a single molecule or a DNA fragment are desirable or required. Thus, cell or biomolecule separation and detection devices and methods should be rapid, sensitive, target specific, highly parallel, and/or comprehensive.
A specific type of cell and biomolecule separation and detection method uses microfluidic devices to conduct high throughput separation and analysis. By designing patterned fluidic channels in the micro or sub-micro scales, often on a small chip, one is able to carry our multiple assays simultaneously. The cells and biomolecules in microfluidic assays typically are detected through optical readout of fluorescent labels attached to a target cell or molecule that is specifically attached or hybridized to a probe molecule. Separation technologies currently used for biomolecules, such as nucleic acid and protein, typically utilize gel electrophoresis or microfluidic channels which typically employ incorporated fluorescent labels or dyes.
Some biomolecule detection methods have been developed based upon the unique electrochemical and photoelectrochemical properties of metal particles. In one assay method, gold nanoparticles (approximately 10 nm diameters) are tagged with ssDNA probe strands and a photoactive dye molecule. A metal electrode of a microarray chip (also called gene chip) is also modified with ssDNA probe strands. If a target (the analyte or bioanalyte) mRNA or ssDNA is complementary to the probe on the particle and the substrate, hybridization will occur which brings the particle in contact with the electrode. A laser is then radiated across the surface. When the laser addresses a spot in which nanoparticles are bound, the dye molecule is electronically excited, and the excited electron is injected into the electrode. The electron is collected as a current, signifying the presence of a particular DNA analyte.
Synthesis of a functionalized electrode having polymer arrays on an electrode of a microarray chip is known. Examples of such polymer arrays include nucleic acid arrays, peptide arrays, and carbohydrate arrays. One method of preparing functionalized electrodes of polymer arrays on microarray chips involves photolithographic techniques using photocleavable protecting groups. Briefly, the method includes attaching photoreactive groups to the surface of a substrate, exposing selected regions of the substrate to light to activate those regions, attaching a monomer with a photoremovable group to the activated regions, and repeating the steps of activation and attachment until macromolecules of a length and sequence are synthesized.